1. Field of the Invention
The present invention relates generally to the field of three dimensional (3-D) displays. More particularly, the present invention concerns 3-D displays that do not require the viewer to wear goggles or glasses. The present invention thus relates to 3-D display systems of the type that can be termed autostereoscopic.
2. Discussion of the Related Art
Stereo vision is based on the perception of depth. Stereo display systems are based on the most dominant depth cue (i.e., parallax), which is defined as the angular separation between corresponding points of left and right perspective images. In this respect, human 3-D vision does not require "real" 3-D information, since the human brain has contact with only two 2-D retinal images, neither of which preserve z-axis (i.e., depth) information. This third dimension is reconstructed only in the brain. Therefore, 3-D displays can be based on capturing and displaying a 2-D left image and a 2-D right image in order to replicate the corresponding left and right retinal images.
In many technical fields, 3-D displays can provide scientists and technicians with the ability to better interpret the physical parameters of an image being displayed. 3-D display techniques have been attempted in the past, but have suffered from the need for the observer to wear external devices, the loss of real-time display capabilities, a lack of full screen resolution, the need for heavy computation and special formatting, very high cost, and/or any combinations of the above. A truly practical device must be able to interface with conventional 2-D display systems in order to increase vendor acceptance, provide real-time capabilities for interactive applications, and provide 3-D look around capabilities without special viewing glasses. In addition, a cost effective production method must be established to make the device attractive for commercial markets.
As noted above, stereoscopic displays provide an observer with parallax depth cues. This is done by presenting each eye with a view of an object from a different perspective viewpoint. When the difference between these viewpoints approximates normal interocular separation, an impression of viewing an actual solid object is created. Conventionally, some form of viewing device, such as glasses, is required to channel a different view into each eye. This is quite effective in presenting a three dimensional impression, and it requires only twice the amount of image data compared to a two dimensional view. The major drawback is the need to wear a device or to peer into eyepieces. This has led to many years of effort to provide directly viewable (i.e., stereoscopic without glasses) or, more precisely, autostereoscopic images.
Autostereoscopic displays create a "window" through which an unaided observer can view what appears to be a solid object. This is a very natural and desirable situation from the standpoint of the observer, but involves two substantial technical challenges. First, the light rays leaving the display must be directed so that each of the observer's eyes receive a complete but different image. Second, images of the object from a range of viewpoints must be presented simultaneously. There may be as few as two perspective views, but typically four or more are required to provide a range of viewing positions (scenes). This greatly increases the amount of image data which must be managed.
Holographic displays and lenticular photographs are the most familiar examples of autostereoscopic images. Holographic displays (or holograms) are an interferometric pattern of a recorded object which can be reconstructed by a collimated beam.
Recently, considerable interest has been directed toward autostereoscopic techniques which are based on the multiplex carrier method. This is because of the simplicity, practicality, and potential low cost of this approach. This technique provides a limited look-around 3-D effect if more than two perspectives are projected into the viewing eye-box. If the number of perspectives is low enough, images may be generated and displayed in real-time because the data processing demands can be satisfied. However, in this technique, the image projection area must be divided into two separate parts, which significantly reduces the image's spatial resolution. Further, this technique has additional drawbacks, because it requires sequential scanning of N perspectives (N&gt;1) for each vertical scan line. The line feed rate R to the multiplexed monitor is related to the flicker-free line rate r by R=N.times.r. Thus, the feed signal rate is increased two or more times relative to the rate necessary for a monocular monitor.
The disclosures of all the below-referenced prior United States patents in their entireties are hereby expressly incorporated by reference into the present application for purposes including, but not limited to, indicating the background of the present invention and illustrating the state of the art. U.S. Pat. No. 3,479,111 discloses a three-dimensional picture projection. U.S. Pat. No. 4,799,739 discloses real time autostereoscopic displays using holographic diffusers. U.S. Pat. No. 4,926,412 discloses a high channel density wavelength division multiplexer with defined diffracting mean positioning. U.S. Pat. No. 5,365,354 discloses a GRIN type diffuser based on volume holographic material.